shebang

Under Unix, if the first two bytes of an executable file
are "#!", the kernel treats the file as a script rather than
a machine code program. The word following the "!" (i.e.,
everything up to the first whitespace) is used as the
pathname of the interpreter. For example, if the first
line of an executable is

#!/usr/local/bin/perl

the script will be treated as a Perl script and passed as an
argument to /usr/local/bin/perl to be interpreted. Some
variants of Unix also allow one or more parameters to be
passed to the interpreter, for example, you can write

#!/usr/bin/perl -w

and the script will be started as if you typed

/usr/bin/perl -w <filename>

on the command line. Also, most modern kernels ignore any
whitespace between the "!" and the interpreter pathname. Even
some modern kernels have fairly small limits (e.g. 32) on the
length of line they will accept, making long pathnames and
arguments somewhat unportable.